1. Field of the Invention
The present invention relates to an airbag unit for protecting people in an automotive vehicle from a lateral-side crashing accident, and more particularly to an airbag unit which is capable of coping with a frontal crashing phenomenon as well as the lateral-side crashing accident, together with a method of inflating the airbag unit provided therein.
2. Description of the Related Art
The conventional airbag unit is a system including an anti-frontal-crash protective device whose configuration is, for example, as simple as the one shown in FIG. 7, so that a so-called anti-frontal-crash protective device (hereinafter may be referred to just as a front-side airbag unit) is first explained here in order to facilitate the understanding about an airbag unit as a whole.
Within the configuration shown in FIG. 7, an electric voltage output from a vehicle mounting type battery 1 is supplied, by way of an ignition switch 2, to a step-up transformer circuit 3, and a back-up capacitor 4 is charged by the thus enhanced output voltage. Thereafter, when a microcomputer 9 (later explained) judges that there has been a serious crash on the basis of an acceleration signal fed from an acceleration sensor 8 and drives a switching circuit 5 to the on state, the electric charge generated at back-up capacitor 4 is discharged by way of a squib 6 and a mechanical acceleration switch 7 (in the on state here, although it is normally in the off state) which are serially connected, and the powder (not shown) is thus exploded by the squib 6, and an airbag is thereby inflated.
However, the anti-frontal-crash protective device has been developed only for protecting the people mounted in a vehicle from a crashing accident caused at the vehicle front portion, whereby in order to protect the people also from a lateral-side crashing force exerted against the lateral side portions of the vehicle, there has also been provided an airbag unit having a configuration shown in FIG. 8 wherein some circuits are commonly used.
Namely, as shown in FIG. 8, the unit denoted by reference numeral 10 is a front-side airbag unit for protecting the people inside the vehicle from a crash caused at the vehicle front portion, the detailed explanation about which is omitted here as the configuration thereof is identical with the one shown in FIG. 7. The unit denoted by reference numeral 11 is a lateral-side airbag unit for driver's seat (hereinafter may be referred to just as a driver's seat airbag unit) arranged for protecting the driver from a crash caused at the lateral side portion, wherein the electric power for this driver's seat airbag unit 11 is supplied by being connected with the back-up capacitor 4 for the above-explained anti-frontal-crash protective device 10 by way of a power line 13 such as a harness or the like through the terminal A. On the other hand, the unit denoted by reference numeral 12 is a lateral-side airbag unit for assistant driver's seat (hereinafter may be referred to just as an assistant driver's seat airbag unit), and the configuration thereof is totally same as that of the driver's seat airbag unit 11.
Reference numeral 20 denotes a microcomputer having the similar function as that of the microcomputer 9, which receives an acceleration signal generated in the lateral direction of the driver's seat and fed from a lateral-direction acceleration sensor 19 (hereinafter abbreviated to a lateral acceleration sensor). When the microcomputer 20 judges that the detected crash is a serious one, it sets a switching circuit 21 to the on state. It should be noted that reference numeral 17 denotes a squib same as the squib 6, reference numeral 18 denotes a mechanically activated acceleration switch same as the switch 7, and reference numeral 15 denotes a constant voltage circuit, which receives an output voltage from the before-mentioned back-up capacitor 4 by way of the power line 13, and provides constant voltage to each of the circuits configuring the driver's seat airbag unit 11.
By the way, the assistant driver's seat airbag unit denoted by reference numeral 12 in FIG. 8 is connected in parallel with the driver's seat airbag unit 11 which is further connected with the terminal A of the before-explained anti-frontal-crash protective device 10. The assistant driver's seat airbag unit 12 is connected with the before-explained anti-frontal-crash protective device 10 by way of a power line 14 through an output terminal A'.
Since the anti-frontal-crash protective device 10 operates just like the one shown in FIG. 7, the detailed explanation thereabout is therefore omitted here. The driver's seat airbag unit 11 receives the enhanced voltage fed from the step-up transformer circuit 3 of the protective device 10 by way of the power line 13 through the output terminal A, and the lateral acceleration sensor 19 thereof detects an acceleration signal generated in response to a lateral crashing force exerted to the driver's seat door. When the microcomputer 20 judges that the crash has been a serious one due to the thus detected signal, it sets the switching circuit 16 to on, so that it sends the electric power, which is charged at the back-up capacitor 4 of the anti-frontal-crash protective device 10 and provided by way of the power line 13, to the squib 17 and the mechanically activated acceleration switch 18 serially, so as to explode powder (not shown) and inflate the airbag.
Further, the assistant driver's seat airbag unit 12 is configured in the substantially same manner as that of the driver's seat airbag unit 11, and just like the driver's seat airbag unit 11, it not only receives the enhanced voltage from the step-up transformer circuit 3 of the anti-frontal-crash protective device 10 by way of the power line 14 through the output terminal A', but the lateral acceleration sensor thereof also detects an acceleration signal generated in response to a lateral crashing force exerted to the assistant driver's seat door. When the microcomputer judges that the crash has been a serious one due to the thus detected signal, it sets the switching circuit to on, so that it sends the electric power, which is charged by the back up capacitor 4 of the anti-frontal-crash protective device 10, to the squib and the acceleration switch serially, thereby to explode powder and inflate the airbag.
However, since each of the airbag units as shown in FIG. 8 is provided with an acceleration sensor, the system size as a whole is made too large, causing thereby a rise of total cost.
Further, in consideration of a precise signal detection, when an acceleration signal generated at the moment of a crash does not abruptly vary; namely the case of an intermediate-speed crash, as is shown in each of the cases of offset crashing, center-pole crashing, right-oblique crashing, left-oblique crashing and so on all possibly caused in the case of a frontal crash, a threshold level which is different from that for a normal high-speed crash should be set. Similarly, in the case of a lateral side crash, considering the case in which acceleration signals are detected by a sensor at a position close to the longitudinal center axis of a vehicle, the acceleration signal generated at the moment of crashing is not likely to be transmitted directly to the sensor. In other words, when an acceleration signal is generated by a lateral crashing force exerted to the side door panel, the crashing energy is converted from an initial destruction force against the vertical surface of the panel to a horizontal bending force, so that the acceleration thereof finally transmitted to the sensor can be defined more likely as the intermediate-speed crash observed in the case of the frontal crash. Therefore, if the threshold for judging the level of danger is set to only one level for all kinds of crash, the magnitude of acceleration cannot be properly detected.